Alcohol esters of triglycerides have been shown to be desirable alternatives for petroleum diesel fuel. One method for producing alcohol esters of vegetable oils involves a transesterification reaction between a vegetable oil and an alcohol. The transesterification reaction is preferably carried out in an excess of the theoretical, stoichiometric quantity of alcohol and a catalyst. The products from the reaction are: (1) an alcohol ester of vegetable oil; (2) by-product alcohol, such as glycerin; (3) unreacted excess alcohol; and (4) residual and spent catalyst. The by-product alcohol is insoluble in the alcohol ester. Accordingly, upon completion of the reaction in a reactor vessel, the reaction products separate into two phases: an ester rich phase and a by-product alcohol rich phase. The unreacted excess alcohol and residual and spent catalyst are distributed between the ester and by-product alcohol rich phases.
An existing process for the production of a methyl ester of rapeseed oil involves reacting excess methyl alcohol with the rapeseed oil. The reaction products are allowed to separate into the ester phase and alcohol phase. The two phases are then separated and then the ester rich phase is washed with water to remove unreacted methyl alcohol, residual catalyst, and spent catalyst. This water washing step requires large volumes of water, the handling of which contributes to the size of the equipment and the expense of operating such equipment. Also, the wash water including the extracted methyl alcohol and the residual and spent catalyst is disposed of without further treatment resulting in a loss of these materials. The wasting of these materials is an economic loss and an environmental disposal problem.
Waste oils and animal fats, for example from meat packing plants, and food processing plants frying oil waste, are also potential sources of raw material for the transesterification reaction to produce alcohol esters. Plentiful sources of these starting materials exist. The purified alcohol esters can be used as fuel alternatives and in other high value end products such as detergent surfactants, herbicides, pesticides diluents, sticking agents, or lubricating additives for hydraulic and transmission fluids.
In view of the increasing interests in alternative fuel sources and other uses of purified alcohol esters, there exists a need for a more economical and environmentally sound process for producing alcohol esters of triglycerides.